Why go heavy?

[Quicksilver]

Beyond the obvious ballistic coefficient increase, what would be the best reason to go from a bullet that works (a 175 SMK in my example) to say a 210 SMK (I have a 1:10 twist barrel, but it is a gas gun) if you already have great results with a 175?

I know my rifle can push a 210, but didn't see any real advantages over the 175 besides the higher B.C.

 

[Bob 964]

Obviously, the heavier bullets will be less subject to wind deflection, especially at longer distances. If you don't shoot long distances, there may not be an advantage to shooting heavier bullets, especially if you have a well-performing 175. Personally, I shoot the heaviest (and longest) bullet my gun will effectively stabilize, using the Miller twist formula. I shoot a 208 Amax out of my Savage 110FP (1:10 twist). I get good velocity (2625 FPS) and it generally goes where I aim it.

 

[Known]

The trick is pushing the heavier bullet fast enough to take advantage of their higher B.C. That's where the 155 Scenar and the newly designed Sierra 155 palma bullets come in handy - you have the same B.C. as the Sierra 175 but you can push them faster because they are lighter. As a result, you have noticeably less drop.

JBM ballistics is a terrific help in this respect: JBM

 

[usafabrad]

A "flatter" trajectory has its advantages in a UKD course where you might have some slop to play with in your range calls. Their "danger space" , that is, their margin for error on either side of a given range call for a given precision requirement, is significantly longer due to their higher velocity.

 

[milo 2.0]

Not to be a smartass, a guy sometimes wonders if we're not trying to shoot a bullet bigger than the case itself, like the 300 blackout???

Using most ballistics programs, one can kind of figure the breakover point of where it will help to achieve what you're trying to accomplish.
There's a point where the speed will overcome the weight and higher bc. Just knowing when and where, and how far you plan to shoot will dictate it.

 

[Ledzep]

There's a bell curve. Given a certain cartridges case volume, it can only push light bullets so fast and you burn more powder doing so, and those light bullets have lower BC. On the other end you push bullets that are so heavy you can't get them to a high enough velocity to keep them supersonic or stable long enough. Somewhere in the middle (usually towards the heavy side) there is a good combo that gets the best of both.

For a .308, it could be 175gr, for a 300wm, 210gr. for example.

 

[jwp6114]

Obviously, the heavier bullets will be less subject to wind deflection, especially at longer distances. If you don't shoot long distances, there may not be an advantage to shooting heavier bullets, especially if you have a well-performing 175. Personally, I shoot the heaviest (and longest) bullet my gun will effectively stabilize, using the Miller twist formula. I shoot a 208 Amax out of my Savage 110FP (1:10 twist). I get good velocity (2625 FPS) and it generally goes where I aim it.

How long is your barrel and what powder are u using sir? I am just beginning to play with the 208's in my 24" 10 twist...

 

[Bob 964]

Barrel is 24". Powder is Alliant PowerPro 2000 MR.

 

[Dan Newberry]

At 2500 fps, the 208's drift about the same as most 6.5's, but the 6.5's trajectory is much flatter--which, as someone else mentioned, is an advantage when shooting at UKD and estimating range.

So in short, for us .308 shooters, the heavy bullets allow us to shoot drift factors equal to (or sometimes better than) the 6mm and 6.5 shooters.

We've just got to be one heck of a lot better at estimating UKD's...

Dan

 

[jwp6114]

I have personally found target ranging easier than wind calling (depending on number of indicators)

The wind at distance is a trickster...

 

[derrelw]

I have personally found target ranging easier than wind calling (depending on number of indicators)

The wind at distance is a trickster...

I'll second that.

 

[Quicksilver]

Thanks for the replies. That's what I was pretty much thinking- the problem is with having a gas gun and NOT having an adjustable gas block, I can't really keep that heavy bullet stable (can't make a good enough charge to get the MV up)- sure the twist rate is good enough to keep it above the "danger zone" (below 1.4) but not by much according to the G7 and other data published by Brian Litz. Im so accustomed to the 175 now that the only thing I might try at this point is "tipping" the bullets... im just not sure if the 300 dollar dies to do it are really worth it.

 

[jwp6114]

I do not recommend some of the tricks that work in bolt guns... Lighter neck tension for example for use in a semi auto...
If you run 1-1.5 thou of neck tension you will surely get bullet movement and inconsistent jump upon firing...

 

[P7id10t]

Why go heavy? BBW do it better, of course!